Central Heating Rumble

Hi, I have a new Vaillant Eco tech plus Combi which is fitted to the outside wall, in the loft.
During pump operation there is a deep rumble noise emminating from the general area in the old airing cupboard on the first floor. It's very difficult to locate a specific position where the noise is. In the loft, I wouldn't say the boiler itself makes a lot more than expected noise and vibration levels (when you place your hand on the case). The noise reduced somewhat, when I opened up the radiator valves fully (not the thermo valves, the other end). The plumber had set most only slightly open.
Could this imply the bypass valve hasn't been set correctly? How do you set this?
Is this noise unusual or just bad luck with the pipework?
It's really begining to get on my nerves as I've tuned in to it.
Thanks, Darren
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I don't mean which screw do I turn, I mean how do I decide when the screw is in the correct position?
Ta
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Is this an automatic bypass valve? I had a vague idea Vaillant was doing automatic bypass valves. At any rate, your CH should have a TRV on all radiators except one ( the one in the same room as the thermostat, as long as you have a thermostat that is! ), so the bypass is redundant. Have you got the manual?
If you have TRV's on all rads, then the bypass is needed, but setting one of the TRV's to max temperature will have the same effect as a bypass valve, so if the rumbling doesn't stop when you wind open one of your TRV's, it may mean your bypass valve isn't the problem.
Try opening one TRV right up.
Andy.
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The installation manual just says that the adjustable by-pass valve screw adjusts the pressure between 170 and 350 mbar. There is no explaination as to how you decide which is the correct "pressure" for each particular installation. I haven't wound it in or out yet to try and estimate it's current position and therefore, setting.
The noise is present in my currant setup of two TRV rads wide open and 1 manual rad. wide open. No room stat, just a timer (to be replaced by combined stat/timer at some point).
I did let all TRVs close up once with the manual valve partially closed and there was extreem vibration in pipework. This is what makes me think it's a "too much flow" type problem.
I tried tech help line but no answer.
Help! It's driving me nuts!
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On 2007-01-02, 19:17 Z, in
Darren wrote:

Could there be an old pipe or drainage pipe partially clogged with dark gray gunk or slim, especially in a pipe that runs vertically downward one or more meters, say, to the first floor? E.g., vertical drainage tubes or pipes can gradually develop gunk or slim over time at one point that causes a partial constriction, and the vertical column of water develops a significant pressure head, until it finally forces itself through the constriction with a surprisingly loud, deep-pitch thumping, banging, knocking, or rumbling noise, somewhat like a bass drum. The pitch is so deep, it permeates through walls, etc., making it hard to pinpoint the exact origin. Running a flexible cable back and forth down the old pipe helps clean out the blockage. Then pour bleach down the pipe to try to kill or clean out some of the slim or mold. If inaccessible, perhaps try a speedometer cable. If still inaccessible, just try pouring bleach down the tube periodically to try to break free and/or kill some of the slim. Typical dirty water, especially if it contains house dust, can eventually form this slim or crud, especially in drainage pipes of diameter 20 mm or less that have a slow trickle and therefore also contain air.
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